CEDAR
Coupling, Energetics and Dynamics of Atmospheric Regions Program
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Implementing Horizontal Viscosity in the Global Ionosphere-Thermosphere Model (GITM)

Atheer
Alhothali
1- Department of Climate and Space Sciences and Engineering, College of Engineering, University of Michigan, Ann Arbor, MI 48109, USA 2-Department of Space Studies, IESS, KACST, Riyadh, Saudi Arabia
Abstract text

Viscosity plays an important role in the thermosphere by damping sharp neutral wind velocity gradients. However, our understanding of its full impact remains incomplete, largely due to numerical considerations in global models. Most current thermosphere models include only the viscosity in the vertical shear, neglecting the contribution from horizontal shear. Horizontal viscosity terms have recently been implemented in the Global Ionosphere-Thermosphere Model (GITM) to represent the full viscous momentum damping in the thermosphere. The horizontal viscosity terms are incorporated into the GITM's momentum equations using a semi-implicit numerical approach, allowing a numerically stable solution. The implementation was tested through simulation targeting conditions with strong horizontal wind shear on the dusk side under strong negative Interplanetary Magnetic Field (IMF) By conditions. The results demonstrated that horizontal viscosity plays a crucial role in smoothing the duskside wind shear; for example, the viscous acceleration of the eastward wind due to meridional shear increased with altitude from ±0.001 m/s² at 149 km to ±0.4 m/s² at 395 km, where the peak eastward wind velocity is reduced by ~100 m/s. These findings highlight the importance of implementing these terms in thermospheric models. This study will present GITM simulations with and without horizontal shear viscosity compared to the High Altitude Interferometer WIND (HIWIND) observations.

Authors
Atheer Alhothali, 1-Department of Climate and Space Sciences and Engineering, College of Engineering, University of Michigan, Ann Arbor, MI, USA 2-Department of Space Studies, IESS, KACST, Riyadh, Saudi Arabia.
Aaron J. Ridley, Department of Climate and Space Sciences and Engineering, College of Engineering, University of Michigan, Ann Arbor, MI, USA
Mojtaba Akhavan-Tafti, Department of Climate and Space Sciences and Engineering, College of Engineering, University of Michigan, Ann Arbor, MI, USA
Chen Wu, Department of Climate and Space Sciences and Engineering, College of Engineering, University of Michigan, Ann Arbor, MI, USA
Shasha Zou, Department of Climate and Space Sciences and Engineering, College of Engineering, University of Michigan, Ann Arbor, MI, USA
Student in poster competition
Poster category
SOLA - Solar Terrestrial Interactions in the Upper Atmosphere
Poster number
7
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